Here is the full list of all 36 Desperados III achievements.
Kill 31 hidden Mimimi devs.
Earn 90 badges.
In the first part of the mission, burn 5 guards at once with oil traps.
Kill 5 guards at once with dynamite.
Kill all 3 golden chickens.
Knock out your father.
Kill 10 small animals in one mission.
Make guards follow Kate for 1,000 meters total.
Jump from a tower into a cart of hay.
Interrupt an important healing procedure.
Kill 200 guards using Cooper's double shot.
Return the money to the bank.
Finish a mission on "Desperado" difficulty.
Enjoy some cupcakes during a picnic.
Kill 6 guards at once using only a single skill.
Complete 5 of the Baron's Challenges.
Mind control 25 guards with Isabelle.
Kill 75 guards with Bianca.
Defeat Frank.
Take care of DeVitt.
Kill DeVitt.
Hide 750 bodies.
Kill 1,000 guards.
Kill 75 Long Coats.
Snipe 50 guards with McCoy.
Meet Frank on a boat.
Kill 15 of the hidden Mimimi devs.
Find Wayne.
Kill 500 guards.
Execute a plan with all five characters.
Kill 50 guards using the environment.
Find a patient for the dentist.
Make someone follow your footprints for 25 meters.
Hide 250 bodies.
Blow up a bridge.
Decide the outcome of a duel.